This invention relates to a novel class of N-formyl hydroxylamine derivatives having antibacterial activity, and to pharmaceutical and veterinary compositions comprising such compounds.
In general, bacterial pathogens are classified as either Gram-positive or Gram-negative. Many antibacterial agents (including antibiotics) are specific against one or other Gram-class of pathogens. Antibacterial agents effective against both Gram-positive and Gram-negative pathogens are therefore generally regarded as having broad-spectrum activity.
Many classes of antibacterial agents are known, including the penicillins and cephalosporins, tetracyclines, sulfonamides, monobactams, fluoroquinolones and quinolones, aminoglycosides, glycopeptides, macrolides, polymyxins, lincosamides, trimethoprim and chloramphenicol. The fundamental mechanisms of action of these antibacterial classes vary.
Bacterial resistance to many known antibacterials is a growing problem. Accordingly there is a continuing need in the art for alternative antibacterial agents, especially those which have mechanisms of action fundamentally different from the known classes.
Amongst the Gram-positive pathogens, such as Staphylococci, Streptococci, Mycobacteria and Enterococci, resistant strains have evolved/arisen which makes them particularly difficult to eradicate. Examples of such strains are methicillin resistant Staphylococcus aureus (MRSA), methicillin resistant coagulase negative Staphylococci (MRCNS), penicillin resistant Streptococcus pneumoniae and multiply resistant Enterococcus faecium. 
Pathogenic bacteria are often resistant to the aminoglycoside, xcex2-lactam (penicillins and cephalosporins), and chloramphenicol types of antibiotic. This resistance involves the enzymatic inactivation of the antibiotic by hydrolysis or by formation of inactive derivatives. The xcex2-lactam (penicillin and cephalosporin) family of antibiotics are characterised by the presence of a xcex2-lactam ring structure. Resistance to this family of antibiotics in clinical isolates is most commonly due to the production of a xe2x80x9cpenicillinasexe2x80x9d (xcex2-lactamase) enzyme by the resistant bacterium which hydrolyses the xcex2-lactam ring thus eliminating its antibacterial activity.
Recently there has been an emergence of vancomycin-resistant strains of enterococci (Woodford N. 1998 Glycopeptide-resistant enterococci: a decade of experience. Journal of Medical Microbiology. 47(10):849-62). Vancomycin-resistant enterococci are particularly hazardous in that they are frequent causes of hospital based infections and are inherently resistant to most antibiotics. Vancomycin works by binding to the terminal D-Ala-D-Ala residues of the cell wall peptidioglycan precursor. The high-level resistance to vancomycin is known as VanA and is conferred by a genes located on a transposable element which alter the terminal residues to D-Ala-D-lac thus reducing the affinity for vancomycin.
In view of the rapid emergence of multidrug-resistant bacteria, the development of antibacterial agents with novel modes of action that are effective against the growing number of resistant bacteria, particularly the vancomycin resistant enterococci and xcex2-lactam antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus, is of utmost importance.
This invention is based on the finding that certain N-formyl hydroxylamine derivatives have antibacterial activity, and makes available a new class of antibacterial agents.
Although it may be of interest to establish the mechanism of action of the compounds with which the invention is concerned, it is their ability to inhibit bacterial growth, which makes them useful. However, it is presently believed that their antibacterial activity is due, at least in part, to intracellular inhibition of bacterial polypeptide deformylase (PDF) enzyme.
Bacterial polypeptide deformylases (PDF) (EC 3.5.1.31), are a conserved family of metalloenzymes (Reviewed: Meinnel T, Lazennec C, Villoing S, Blanquet S, 1997, Journal of Molecular Biology 267, 749-761) which are essential for bacterial viability, their function being to remove the formyl group from the N-terminal methionine residue of ribosome-synthesised proteins in eubacteria. Mazel et al. (EMBO J. 13(4):914-923, 1994) have recently cloned and characterised an E. coli PDF. As PDF is essential to the growth of bacteria and there is no eukaryotic counterpart to PDF, Mazel et al. (ibid), Rajagopalan et al. (J. Am. Chem. Soc. 119:12418-12419, 1997) and Beckeretal., (J. Biol Chem. 273(19):11413-11416, 1998) have each proposed that PDF is an excellent anti-bacterial target.
Certain N-formyl hydroxylamine derivatives have previously been claimed in the patent publications listed below, although very few examples of such compounds have been specifically made and described:
EP-B-0236872 (Roche)
WO 92/09563 (Glycomed)
WO 92/04735 (Syntex)
WO 95/19965 (Glycomed)
WO 95/22966 (Sanofi Winthrop)
WO 95/33709 (Roche)
WO 96/23791 (Syntex)
WO 96/16027 (Syntex/Agouron)
WO 97/03783 (British Biotech)
WO 97/18207 (DuPont Merck)
WO 98/38179 (GlaxoWelicome)
WO 98/47863 (Labs Jaques Logeais)
The pharmaceutical utility ascribed to the N-formyl hydroxylamine derivatives in those publications is the ability to inhibit matrix metalloproteinases (MMPs) and in some cases release of tumour necrosis factor (TNF), and hence the treatment of diseases or conditions mediated by those enzymes, such as cancer and rheumatoid arthritis. That prior art does not disclose or imply that N-formyl hydroxylamine derivatives have antibacterial activity.
In addition to these, U.S. Pat. No. 4,738,803 (Roques et al.) also discloses N-formyl hydroxylamine derivatives, however, these compounds are disclosed as enkephalinase inhibitors and are proposed for use as antidepressants and hypotensive agents. Also, WO 97/38705 (Bristol-Myers Squibb) discloses certain N-formyl hydroxylamine derivatives as enkephalinase and angiotensin converting enzyme inhibitors. This prior art does not disclose or imply that N-formyl hydroxylamine derivatives have antibacterial activity either.
Our copending International patent application no. PCT/GB99/00386 discloses that certain N-formyl hydroxylamine derivatives have antibacterial activity. One class of compounds disclosed as having such activity has general formula (IA): 
wherein the various xe2x80x9cRxe2x80x9d substituents are as specified in the document. The compounds useful in accordance with the present invention differ in structure from those of PCT/GB99/00386 principally in that the acyclic amidoalkyl radical shown as lying to the right of the curved line in formula (IA) is replaced by a cyclic radical.
According to the first aspect of the present invention there is provided a compound of formula (I) or a pharmaceutically or veterinarily acceptable salt, hydrate or solvate thereof: 
wherein:
R1 represents hydrogen, methyl, or trifluoromethyl
R2 represents a group R10-(X)n-(ALK)- wherein
Rl, represents hydrogen, a C1-C6 alkyl, C2-C alkenyl, C2-C6 alkynyl, cycloalkyl, aryl, or heterocyclyl group, any of which may be unsubstituted or substituted by (C1-C6)alkyl, (C1-C6)alkoxy, hydroxy, mercapto, (C1-C6)alkylthio, amino, halo (including fluoro, chloro, bromo and iodo), trifluoromethyl, cyano, nitro, -COOH, -CONH2, -COORA, -NHCORA, -CONHRA, -NHRA, -NRAR, or -CONRARB wherein RA and RB are independently a (C1-C6)alkyl group, and
ALK represents a straight or branched divalent C1-C6 alkylene, C2-C6 alkenylene, C2-C6 alkynylene radical, and may be interrupted by one or more non-adjacent xe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94 linkages,
X represents xe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94, and
n is 0 or 1; and
R3 and R4, taken together with the carbon atoms to which they are respectively attached, form an optionally substituted saturated carbocyclic or heterocyclic ring of 5 to 16 atoms, which may be benz-fused or fused to a second optionally substituted saturated carbocyclic or heterocyclic ring of 5 to 16 atoms.
In another aspect, the invention provides the use of a compound of formula (I) as defined above in the preparation of a composition for treatment of bacterial infections in humans and non-human mammals.
In another aspect, the invention provides a method for the treatment of bacterial infections in humans and non-human mammals, which comprises administering to a subject suffering such infection an antibacterially effective dose of a compound of formula (I) as defined above.
In a further aspect of the invention there is provided a method for the treatment of bacterial contamination by applying an antibacterially effective amount of a compound of formula (I) as defined above to the site of contamination.
The compounds of formula (I) as defined above may be used as component(s) of antibacterial cleaning or disinfecting materials.
On the hypothesis that the compounds (I) act by inhibition of intracellular PDF, the most potent antibacterial effect may be achieved by using compounds which efficiently pass through the bacterial cell wall. Thus, compounds which are highly active as inhibitors of PDF in vitro and which penetrate bacterial cells are preferred for use in accordance with the invention. It is to be expected that the antibacterial potency of compounds which are potent inhibitors of the PDF enzyme in vitro, but are poorly cell penetrant, may be improved by their use in the form of a prodrug, ie a structurally modified analogue which is converted to the parent molecule of formula (I), for example by enzymic action, after it has passed through the bacterial cell wall.
As used herein the term xe2x80x9c(C1-C6)alkylxe2x80x9d means a straight or branched chain alkyl moiety having from 1 to 6 carbon atoms, including for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl and n-hexyl.
As used herein the term xe2x80x9cdivalent (C1-C6)alkylene radicalxe2x80x9d means a saturated hydrocarbon chain having from 1 to 6 carbon atoms and two unsatisfied valencies.
As used herein the term xe2x80x9c(C2-C6)alkenylxe2x80x9d means a straight or branched chain alkenyl moiety having from 2 to 6 carbon atoms having at least one double bond of either E or Z stereochemistry where applicable. The term includes, for example, vinyl, allyl, 1- and 2-butenyl and 2-methyl-2-propenyl.
As used herein the term xe2x80x9cdivalent (C2-C6)alkenylene radicalxe2x80x9d means a hydrocarbon chain having from 2 to 6 carbon atoms, at least one double bond, and two unsatisfied valencies.
As used herein the term xe2x80x9cC2-C6 alkynylxe2x80x9d refers to straight chain or branched chain hydrocarbon groups having from two to six carbon atoms and having in addition one triple bond. This term would include for example, ethynyl, 1-propynyl, 1- and 2-butynyl, 2-methyl-2-propynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl and 5-hexynyl.
As used herein the term xe2x80x9cdivalent (C2-C6)alkynylene radicalxe2x80x9d means a hydrocarbon chain having from 2 to 6 carbon atoms, at least one triple bond, and two unsatisfied valencies.
As used herein the term xe2x80x9ccycloalkylxe2x80x9d means a saturated alicyclic moiety having from 3-8 carbon atoms and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.
As used herein the term xe2x80x9ccycloalkenylxe2x80x9d means an unsaturated alicyclic moiety having from 3-8 carbon atoms and includes, for example, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl and cyclooctenyl. In the case of cycloalkenyl rings of from 5-8 carbon atoms, the ring may contain more than one double bond.
As used herein the term xe2x80x9carylxe2x80x9d refers to a mono-, bi- or tri-cyclic carbocyclic aromatic group, and to groups consisting of two covalently linked monocyclic carbocyclic aromatic groups. Illustrative of such groups are phenyl, biphenyl and napthyl.
As used herein the term xe2x80x9cheteroarylxe2x80x9d refers to a 5- or 6-membered aromatic ring containing one or more heteroatoms, and optionally fused to a benzyl or pyridyl ring; and to groups consisting of two covalently linked 5- or 6-membered aromatic rings each containing one or more heteroatoms; and to groups consisting of a monocyclic carbocyclic aromatic group covalently linked to a 5- or 6-membered aromatic rings containing one or more heteroatoms. Illustrative of such groups are thienyl, furyl, pyrrolyl, imidazolyl, benzimidazolyl, thiazolyl, pyrazolyl, isoxazolyl, isothiazolyl, triazolyl, thiadiazolyl, oxadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, 4-([1,2,3]-thiadiazoly4-yl)phenyl and 5-isoxazol-3-ylthienyl.
As used herein the unqualified term xe2x80x9ccarbocyclylxe2x80x9d or xe2x80x9ccarbocyclicxe2x80x9d refers to a 5-8 membered ring whose ring atoms are all carbon.
As used herein the unqualified term xe2x80x9cheterocyclylxe2x80x9d or xe2x80x9cheterocyclicxe2x80x9d includes xe2x80x9cheteroarylxe2x80x9d as defined above, and in particular means a 5-8 membered aromatic or non-aromatic heterocyclic ring containing one or more heteroatoms selected from S, N and O, and optionally fused to a benzene ring, including for example, pyrrolyl, furyl, thienyl, piperidinyl, imidazolyl, oxazolyl, thiazolyl, thiadiazolyl, thiazepinyl, pyrazolyl, pyridinyl, pyrrolidinyl, pyrimidinyl, morpholinyl, piperazinyl, indolyl, benzimidazolyl, maleimido, succinimido, phthalimido and 1,3-dioxo-1,3-dihydro-isoindol-2-yl groups.
Unless otherwise specified in the context in which it occurs, the term xe2x80x9csubstitutedxe2x80x9d as applied to any moiety herein means substituted with up to four substituents, each of which independently may be (C1-C6)alkyl, benzyl, (C1-C6)alkoxy, phenoxy, hydroxy, mercapto, (C1-C6)alkylthio, amino, halo (including fluoro, chloro, bromo and iodo), trifluoromethyl, nitro, -COOH, -CONH2, -CORA, -COORA, -NHCORA, -CONHRA, -NHRA, -NRARB, or -CONRARB wherein RA and RB are independently a (C1-C6)alkyl group. In the case where xe2x80x9csubstitutedxe2x80x9d means benzyl, the phenyl ring thereof may itself be substituted with any of the foregoing, except benzyl.
There are at least two actual or potential chiral centres in the compounds according to the invention because of the presence of asymmetric carbon atoms. The presence of several asymmetric carbon atoms gives rise to a number of diastereoisomers with R or S stereochemistry at each chiral centre. The invention includes all such diastereoisomers and mixtures thereof. Currently, the preferred stereoconfiguration of the carbon atom carrying the R2 group is R; and that of the carbon atom carrying the R1 group (when asymmetric) is R.
In the compounds of formula (1) as defined above:
R1 may be, for example, hydrogen, methyl, or trifuoromethyl. Hydrogen is currently preferred.
R2 may be, for example:
optionally substituted C1-C8 alkyl, C3-C6 alkenyl, C3-C6 alkynyl or cycloalkyl;
phenyl(C1-C6 alkyld, phenyl(C3-C6 alkenyl)- or phenyl(C3-C6 alkynyl)- optionally substituted in the phenyl ring;
cycloalkyl(C1-C6 alkyl)-, cycloalkyl(C3-C6 alkenyl)- or cycloalkyl(C3-C6 alkynyl)- optionally substituted in the cycloalkyl ring;
heterocyclyl(C1-C6 alkyl)-, heterocyclyl (C3-C6 alkenyl)- or heterocyclyl(C3-C6 alkynyl)- optionally substituted in the heterocyclyl ring; or
CH3(CH2)pO(CH2)q- or CH3(CH2)pS(CH2)q-, wherein p is 0, 1, 2 or 3 and q is 1, 2or 3.
Thus, R2 may be, for example,
C1-C6 alkyl, C3-C6 alkenyl or C3-C6 alkynyl;
phenyl(C1-C6 alkyl)-, phenyl(C3-C6 alkenyl)- or phenyl (C3-C6 alkynyl)-optionally substituted in the phenyl ring;
cycloalkyl(C1-C6 alkyl)-, cycloalkyl(C3-C6 alkenyl)- or cycloalkyl(C3-C6 alkynyl)- optionally substituted in the phenyl ring;
heterocyclyl(C1-C, alkyl)-, heterocyclyl(C3-C6 alkenyl)- or heterocyclyl(C3-C6 alkynyl)- optionally substituted in the heterocyclyl ring; or
4-phenylphenyl(C1-C6 alkyl)-, 4-phenylphenyl(C3-C6 alkenyl)-, 4-phenylphenyl(C3-C6 alkynyl)-, 4-heteroarylphenyl(C1-C6 alkyl)-, 4-heteroarylphenyl(C3-C6 alkenyl)-, 4-heteroarylphenyl(C3-C6 alkynyl)-, optionally substituted in the terminal phenyl or heteroaryl ring.
Specific examples of R2 groups include methyl, ethyl, n- and iso-propyl, n- and iso-butyl, n-pentyl, iso-pentyl 3-methyl-but-1-yl, n-hexyl, n-heptyl, n-acetyl, n-octyl, methylsulfanylethyl, ethylsulfanylmethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-ethoxymethyl, 3-hydroxypropyl, allyl, 3-phenylprop-3-en-1-yl, prop-2-yn-1-yl, 3-phenylprop-2-yn-1-yl, 3-(2-chlorophenyl)prop-2-yn-1-yl, but-2-yn-1-yl, cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylpropyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylpropyl, furan-2-ylmethyl, furan-3-methyl, tetrahydrofuran-2-ylmethyl, tetrahydrofuran-2-ylmethyl, piperidinylmethyl, phenylpropyl, 4-chlorophenylpropyl, 4-methylphenylpropyl, 4-methoxyphenylpropyl, benzyl, 4-chlorobenzyl, 4-methylbenzyl, or 4-methoxybenzyl.
Presently preferred groups at R2 are n-propyl, n-butyl, n-pentyl, benzyl and cyclopentylmethyl.
R3 and R4, taken together with the carbon atoms to which they are respectively attached, form an optionally substituted monocyclic saturated carbocyclic or heterocyclic ring of 5 to 16 atoms, for example from 5 to 8 atoms. Referring to formula (I), the carbon atom shown as carrying the group R3 is the one linking the ring to the rest of the molecule, and may arbitrarily be numbered as the 1- position in the ring. The carbon atom shown as carrying the R4 group is adjacent the 1-position, and is oxo- (keto-) substituted. The remaining atoms in the ring may all be carbons, or may include one or more hetero atoms xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94N(R5)xe2x80x94 wherein R5 may be hydrogen, a C1-C4alkyl group, a phenyl or benzyl group, or an acyl radical (for example phenylcarbonyl) or sulphonyl radical (for example 4-methoxyphenylsulphonyl or 4-trifluoromethylphenylsulphonyl).
More than one hetero-atom may be present in the ring, but it will be appreciated that unstable combinations such as adjacent xe2x80x94Oxe2x80x94 atoms will not be feasible. Where the ring contains an S atom, it may be oxidised as a sulphinyl or sulphonyl. In one particular embodiment, the ring atom in the 3-position is xe2x80x94N(R5)xe2x80x94 wherein R5 may be hydrogen or a C1-C4alkyl, phenyl or benzyl group. In another embodiment the ring contains one xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94 atom. In still another embodiment the ring contains one xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94 atom and a nitrogen atom separated by carbon atom(s). In yet another embodiment, the ring contains two or three nitrogen atoms.
In general, the radical formed by R3 and R4, taken together with the carbon atoms to which they are respectively attached may be represented schematically as formula (II) 
wherein rings A and B each have 5-8 ring atoms which may include heteroatoms and which may each be substituted. Ring B is optional, and may be a fused benzene ring or a second 5-8 membered saturated carbocyclic or heterocyclic ring.
The ring formed by R3 and R4, taken together with the carbon atoms to which they are respectively attached, may be substituted (as defined above). In one particular embodiment the ring atom in position n of an n-membered ring (n being 5, 6, 7 or 8 and numbering from position 1, with the oxo-substituted carbon atom being position 2) may be a carbon atom substituted by one or two methyl groups, and the ring atom in position n-1 may be a sulphur atom. Examples of such rings, formed by R3 and R4, taken together with the carbon atoms to which they are respectively attached, are those of the following structure (III): 
wherein R8 may be hydrogen or a C1-C4alkyl (eg methyl, ethyl or n-propyl), cycloalkyl (eg cyclopentyl) phenyl or benzyl group, and R, may be hydrogen or a C1-C4alkyl (eg isobutyl), phenyl or benzyl group, or R8 and R9 taken together represent a divalent xe2x80x94(CH2)pxe2x80x94 radical wherein p is 3 or 4.
Specific examples of radicals having the general structure (II) include
4,7,7-trimethyl-5-oxo-[1,4]thiazepan-6-yl
3-benzyl4,7,7- trimethyl-5-oxo-[1,4]thiazepan-6-yl
3,3-dimethyl-5-oxo- hexahydro-pyrrolo[2,1-c][1,4]thiazepin4-yl
7,7-dimethyl-5-oxo- octahydro-8-thia-4a-aza-benzocyclohepten-6-yl
7,7-dimethyl-5-oxo-octahydro-8-thia4a-aza-benzocycloocten-6-yl
4-ethyl-7,7-dimethyl-5- oxo-[1,4]thiazepan-6-yl
7,7-dimethyl-5-oxo4-propyl-[1,4]thiazepan-6-yl
7,7-dimethyl-5-oxo4-phenyl-[1,4]thiazepan-6-yl
7,7-dimethyl-5-oxo-4- phenyl-[1,4]thiazepan-6-yl
1-methyl-2-oxo-azepan-3-yl
1-benzyl-2-oxo-piperidin-3-yl
1-methyl-2,5-dioxo-pyrrolidin-3-yl
4-methyl-3,5-dioxo-[1,4]oxazepan-6-yl
4-methyl-3,5-dioxo-[1,4]thiazepan-6-yl
1-methyl-2,7-dioxo-azepan-3-yl
1-methyl-2,6-dioxo-piperidin-3-yl
1-methyl-2-oxo-1,2,3,4-tetrahydro-quinolin-3-yl
2-methyl-3-oxo-2,3,4,5-tetrahydro-1H-benzo[c]azepin4-yl
1-methyl-2-oxo-2,3,4,5-tetrahydro-1H-benzo[b]azepin-3-yl
9-methyl-8-oxo-6,7,8,9-tetrahydro-5-oxa-9-aza-benzocyclohepten-7-yl
1-methyl-7-oxo-[1,4]diazepan-6-yl
1-(4-methoxy-benzenesulfonyl)4-methyl-5-oxo-[1,4]diazepan-6-yl
1-benzoyl-4-methyl-5-oxo-[1,4]diazepan-6-yl
1,4-dimethyl-5-oxo-[1,4]diazepan-6-yl
3-benzyl-5-oxo-[1,4]thiazepan-6-yl
3-benzyl-4-methyl-1,1,5-trioxo-[1,4]thiazepan-6-yl
2-benzyl-7-oxo-[1,4]oxathiepan-6-yl and
4-oxo-thiepan-3-yl.
Specific examples of compounds of the invention include those specifically named and characterised in the Examples herein.
Compounds of the invention may be prepared by a process comprising coupling an acid of formula (IV) with an amine of formula (V) 
wherein R1, R2, R3 and R4 are as defined in relation to formula (I). The N-hydroxy group of compound (IV) is preferably protected during the coupling reaction, and the hydroxy group subsequently regenerated.
Compounds of formula (V) may be prepared by cyclisation of compounds of formula (VA) 
wherein one of R13 and R14 contains a reactive group capable of reacting with a reactive partner site on the other of R13 and R14 to form a covalent bond between R13 and R14, thereby forming the desired ring, represented in formula (1) by R3 and R4 taken together with the carbon atoms to which they are respectively attached. During this cyclisation reaction, the amino group of (VA) will usually be protected, and the amino group subsequently released. Such intramolecular cyclisations, for example intramolecular condensation reactions, are known in the synthetic chemistry art. Alternatively, compounds of formula (V) may be prepared by reaction of a compound of formula (VB) 
with a bifunctional linker schematically represented as X1xe2x80x94Lxe2x80x94X2, wherein X1 is a reactive group capable of reacting with a reactive partner site in R23, X2 is a reactive group capable of reacting with a reactive partner site in R24, and R23, R24 and L are chosen such that after reaction of X1 and X2 with their respective reactive partner sites, L forms a covalently linked bridge between R23 and R24 and completes the desired ring, represented in formula (I) by R3 and R4 taken together with the carbon atoms to which they are respectively attached. Again, during this cyclisation reaction, the amino group of (VA) will usually be protected, and the amino group subsequently released.
Again such intra molecular cyclisation by ring formation is known in the art of synthetic chemistry. Example 1 below is one illustration of such a reaction. Such reactions are preferably carried out at high dilution to maximise intramolecular rather than intermolecular bridge formation.
Compounds of the invention may also be accessible by cyclisation of a compound of formula (VI) 
wherein R1 and R2 are as defined in relation to formula (1), and R13 and R14 are as defined in relation to formula (VA). Preferably the N-formyl hydroxylamine group in (VI) is protected during the cyclisation reaction and the protecting group subsequently removed, or may be attached to a solid phase support (eg a resin), and subsequently released.
Alternatively, compounds of the invention may be accessible by reaction of a compound of formula (VIA) 
with a bifunctional linker schematically represented as X1xe2x80x94Lxe2x80x94X2, wherein R1 and R2 are as defined in relation to formula (1), and X1, X2 and L are as defined in relation to formula (VB). Preferably the N-formyl hydroxylamine group in (V) is protected during the bridging reaction and the protecting group subsequently removed, or may be attached to a solid phase support (eg a resin), and subsequently released.
Antibacterial compositions with which the invention is concerned may be prepared for administration by any route consistent with the pharmacokinetic properties of the active ingredient(s).
Orally administrable compositions may be in the form of tablets, capsules, powders, granules, lozenges, liquid or gel preparations, such as oral, topical, or sterile parenteral solutions or suspensions. Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinyl-pyrrolidone; fillers for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricant, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants for example potato starch, or acceptable wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, glucose syrup, gelatin hydrogenated edible fats; emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters such as glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents.
For topical application to the skin, the active ingredient(s) may be made up into a cream, lotion or ointment. Cream or ointment formulations which may be used for the drug are conventional formulations well known in the art, for example as described in standard textbooks of pharmaceutics such as the British Pharmacopoeia.
The active ingredient(s) may also be administered parenterally in a sterile medium. Depending on the vehicle and concentration used, the drug can either be suspended or dissolved in the vehicle. Advantageously, adjuvants such as a local anaesthetic, preservative and buffering agents can be dissolved in the vehicle. Intra-venous infusion is another route of administration for the compounds used in accordance with the invention.
Safe and effective dosages for different classes of patient and for different disease states will be determined by clinical trial as is required in the art. It will be understood that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, rate of excretion, drug combination and the severity of the particular disease undergoing therapy.
The finding that compounds with PDF inhibitory activity can inhibit or prevent bacterial growth, opens up a novel approach for identifying new antibacterial agents by screening test compounds for activity as inhibitors of PDF in vitro, followed by confirmation of their antibacterial ability using bacterial growth inhibition studies. This finding also makes available (i) the use of compounds with PDF inhibitory activity as antibacterial agents, and (ii) a method for the treatment of bacterial infection or contamination by applying or administering a compound which inhibits the activity of bacterial PDF.